title: Gas exchange patterns and water loss rates in the Table Mountain cockroach, Aptera fusca (Blattodea: Blaberidae).
abstract: The importance of metabolic rate and/or spiracle modulation for saving respiratory water is contentious. One major explanation for gas exchange pattern variation in terrestrial insects is to effect a respiratory water loss (RWL) saving. To test this, we measured the rates of CO2 and H2O release ( and , respectively) in a previously unstudied, mesic cockroach, Aptera fusca, and compared gas exchange and water loss parameters among the major gas exchange patterns (continuous, cyclic, discontinuous gas exchange) at a range of temperatures. Mean , and per unit did not differ among the gas exchange patterns at all temperatures (P>0.09). There was no significant association between temperature and gas exchange pattern type (P=0.63). Percentage of RWL (relative to total water loss) was typically low (9.79±1.84%) and did not differ significantly among gas exchange patterns at 15°C (P=0.26). The method of estimation had a large impact on the percentage of RWL, and of the three techniques investigated (traditional, regression and hyperoxic switch), the traditional method generally performed best. In many respects, A. fusca has typical gas exchange for what might be expected from other insects studied to date (e.g. , , RWL and cuticular water loss). However, we found for A. fusca that expressed as a function of metabolic rate was significantly higher than the expected consensus relationship for insects, suggesting it is under considerable pressure to save water. Despite this, we found no consistent evidence supporting the conclusion that transitions in pattern type yield reductions in RWL in this mesic cockroach.
authors.affiliation: Department of Conservation Ecology and Entomology, Centre for Invasion Biology, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa.
authors.forename: Berlizé
authors.initials: B
authors.lastname: Groenewald
authors.forename: Corinna S
authors.initials: CS
authors.lastname: Bazelet
authors.forename: C Paige
authors.initials: CP
authors.lastname: Potter
authors.forename: John S
authors.initials: JS
authors.lastname: Terblanche
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001481:Basal Metabolism / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D003058:Cockroaches / Q000502:physiology*; D017753:Ecosystem; D005260:Female; D005740:Gases / Q000378:metabolism*; D016014:Linear Models; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D015203:Reproducibility of Results; D013019:South Africa; D013696:Temperature; D014867:Water; D014870:Water Loss, Insensible / Q000502:physiology*
chemical_list: D005740:Gases; D014867:Water; D002245:Carbon Dioxide; D010100:Oxygen
keywords: hyperoxic switch method; metabolic efficiency; metabolic rates; regression method; water conservation